I normally sign with the idea of where is the picture going to go in mind. I normally sign with that user name, or a version of it. Other than that, if I don't have an idea, I do not sign work, and at my school, it is discouraged to sign the work,which I find a bit odd, but easy to not have to change habit. At some point I probably should start signing my art, or have something that is distinctively my idea, like hiding a animal in all artwork that is to be published, or I find worthy.